I was led to believe the current state of the Source's aether would make Black Rose more conductive and therefore effective, rather than if it were still normal where the gas would possibly be diluted by the aether by some degree otherwise. I'm not sure that the two were supposed to really "interact", per se. Nevertheless, it's still a big threat in either case. It's also certainly possible that Solus could use it to usurp Zeno-bus, but to date we can't say for sure what his loyalties are to him. While he has attested to the belief that Elidibus has made good judgements toward their cause, he also seemed almost bitter at the prospect of being dragged back to clean up after Lahabrea's misadventures, and he also seemed to regret that his work with Garlemald hasn't lived nearly enough up to the Allagan Empire's legacy. Does this mean he wants to keep building things up and become an emperor again, and maybe extend his rule across all of Hydaelyn? Perhaps, but we cannot say for certain at present. The fact of the matter is that Solus is still shrouded in a lot of mystery, despite what we've learned of him these last couple patches. The finale of the 4.5 story quests may elucidate further into his nature, but until then we still have little to speculate with where he's concerned.

Where the balance between light and darkness is concerned, it's also hard to say what's happening there despite having a little more knowledge about the subject. So far, although noticeable to those versed in such things, for the most part the apparent thinning of aether has been pretty subtle to others. It's a concern, certainly, but it's effects haven't become severe... Yet, that is. While the Ascians had done fairly well at sowing chaos, the WoL has also managed to slay many primals, including Bahamut in the context of those raids, which had a huge effect on the Source's aether. There's also the fact that a lot of the strife caused by the Dragonsong War is gradually diminishing due to our influence, and Ascians have now started to fall for good over time since the Seventh Astral Era began. Add to that Doma's liberation and restoration and, to a lesser degree, Ala Mhigo's as well, and the cumulative effects of all these events would certainly influence the balance. Still, I doubt these events alone could tip the scales so radically as to cause a Flood of Light. No, I suspect there's far more to it. Were Elidibus to be destroyed indefinitely, that could very well be the push that could start a Flood. And how does it all tie in with Black Rose and the final Calamity, exactly? That also could be any number of things. But I'm almost positive that the catalyst that sets things over the brink will be the confrontation with Elidibus when the next bit of story comes out.